docs: fix a few simple typos

[timgates42]

There are small typos in:

• docs/sphinxext/ipython_console_highlighting.py
• docs/sphinxext/ipython_directive.py
• quantecon/compute_fp.py
• quantecon/estspec.py
• quantecon/filter.py
• quantecon/game_theory/pure_nash.py
• quantecon/game_theory/tests/test_vertex_enumeration.py
• quantecon/game_theory/vertex_enumeration.py
• quantecon/lqcontrol.py
• quantecon/lss.py
• quantecon/markov/tests/test_ddp.py
• quantecon/tests/test_ivp.py
• quantecon/util/notebooks.py

Fixes:

• Should read approximation rather than approxmation.
• Should read response rather than reponse.
• Should read frequencies rather than frequences.
• Should read typically rather than typicaly.
• Should read theorem rather than theorm.
• Should read symmetric rather than symetric.
• Should read representing rather than reprensenting.
• Should read parametric rather than parameteric.
• Should read original rather than orignal.
• Should read equilibrium rather than equilibirum.
• Should read default rather than defualt.
• Should read array rather than arrray.
• Should read covariance rather than convariance.

Closes #583

[oyamad]

@timgates42 Thanks!

[coveralls]

Coverage remained the same at 94.424% when pulling 443681c on timgates42:bugfix_typos into 708a699 on QuantEcon:master.

[mmcky]

thanks @timgates42